1. Field of the Invention
The present invention relates to an ink jet recording head, an ink jet recording apparatus and a wiping method therefor.
2. Related Background Art
The ink jet recording method achieves recording by discharging a droplet of recording liquid called ink, and depositing said droplet onto a recording medium. In the field of ink jet recording, there is known a structure in which a recording head is mounted on a carriage capable of scanning motion relative to the recording medium, said recording head being provided with a discharge port or ports for discharging liquid droplet, a liquid path communicating with each discharge port and having an energy generating member for forming the flying liquid droplet, and a liquid chamber communicating with said liquid paths and storing liquid to be supplied to said liquid paths.
There are already known various types of recording head, according to the method of liquid discharge.
Among these, the recording head of a type for providing the ink with thermal energy to generate a bubble therein and effecting the ink discharge by the state change of said bubble is advantageous in that the thermal energy generating elements and functional devices for driving said elements can be prepared in a process similar to that for preparing semiconductor devices, and the discharge ports for ink discharge and the liquid paths which communicate with said discharge ports and in which thermal energy is applied can be prepared by a micro-fabrication process.
Because of this fact, it is possible to increase the density of discharge ports in a recording head, responding for example to the requirements of improvement in the quality of recorded image and increase in the recording speed.
However, in such high-density recording head, the discharge ports have to be prepared uniformly with sufficient precision, since otherwise the direction of ink discharge becomes deflected, thereby deteriorating the quality of the recorded image.
Therefore, in order to easily ensure the precision of the form of discharge ports governing the liquid discharging performance, there has been proposed a method of forming the discharge ports and the discharge plane by adhering an orifice plate, or a discharge port forming member, in which the discharge ports are prefabricated, onto a plane having apertures communicating with the ink liquid chamber.
In such orifice plate, the discharge ports can be formed for example with excimer laser irradiation or a photoetching process with sufficient precision, so that the recording head can be given highly precise discharge ports.
Also such orifice plate is employed for preventing deflection in the liquid discharge resulting from difference in wetting property when the discharge plane is composed of plural members.
In the following there will be briefly explained an example of the conventional structure of a recording head and the method of preparation thereof, with reference to the attached drawings.
At first, on a substrate 131 (for example made of silica glass) on which arranged are discharge energy generating elements (for example electrothermal converting elements such as heat generating resistors for generating thermal energy) 132, as shown in a schematic perspective view in FIG. 1A, there are formed liquid path walls 133 and an outer frame 134 with a hardened film of photosensitive resin as shown in FIG. 1B, and a cover plate 135 provided with a filter 137 in an ink supply hole 136 is laminated thereon. The obtained laminate structure is cut and divided along a line C--C', in order to optimize the distance from the ink discharge ports to the energy generating elements 132, thereby obtaining an intermediate structure of the recording head.
Thereafter, as shown in a perspective assembly view in FIG. 1C, an orifice plate 138 is adhered to the cut plane of said intermediate structure. The orifice plate 138 is composed of a resinous material or a metal, and is provided for improving the ink discharge performance as explained before.
The recording head thus prepared is assembled in the ink jet recording apparatus.
In the above-explained structure, however, the orifice plate has to be very thin, on the order of several microns, in consideration of the discharge characteristics. Because of this fact, there are encountered various difficulties in maintaining the orifice plate in contact with the main body of the recording head.
For example, if the orifice plate is adhered to the aperture plane with an adhesive material, the discharge ports may be clogged by said adhesive material penetrating into the liquid paths by capillary action from the vicinity of the apertures.
In order to prevent such phenomenon, the adhesive material is not used around said apertures, and the orifice plate is maintained in contact with the aperture plane for example with a pressure plate.
On the other hand, in the ink jet recording apparatus, the face of discharge ports may be wetted by a portion of the ink droplets or satellite droplets scattered in the air, or the ink splashing back from the recording medium. Similar wetting may be caused by the moisture evaporated from the recording medium for accelerating the image fixation and condensed on said face of the discharge ports. Such wetting on the discharge port face undesirably affects the discharge performance, such as deflected discharge, and is generally eliminated by a wiping operation.
However, the recording head having the discharge face formed with such orifice plate may pose various problems in the wiping operation. For example the mechanical force of wiping, being exerted repeatedly on the orifice plate, may result in peeling thereof from the plane of apertures. Also the ink removed by wiping may be deposited between the orifice plate and the pressing member therefor, thus eventually clogging the discharge ports.
Furthermore, the conventional ink jet recording head explained above is often associated with following drawbacks:
(1) A cleaning operation with a wiping member is generally required for preventing discharge failure, unevenness in density etc, resulting from deposition of ink or dust in the discharge ports, but the contact of said wiping member with the orifice plate may result in peeling thereof or scraping of said wiping member at the edge of the recording head, thereby generating dusts and deteriorating the durability or reliability of not only the wiping member but also the recording head itself; PA1 (2) The adhesive material usually employed in adhering the orifice plate to the recording head tends to penetrate into the liquid paths, thus eventually clogging said liquid paths. Thus the recording head is poor in production yield and in mass producibility; and PA1 (3) If the adhesive material is not used around the ink discharge ports in order to present penetration of the adhesive material into the liquid paths and to prevent the low mass producibility resulting from the difficulty in the adhering operation, there may be formed a gap between the orifice plate and the recording head, thus giving rise to ink deposition therein and undesirably affecting the stability of ink discharge.